Methods and apparatus for polishing a notch of a substrate by substrate vibration

ABSTRACT

Apparatus and methods are provided for polishing a notch on an edge of a substrate. An exemplary apparatus may include a substrate support adapted to support a substrate; a polishing head adapted to contact a notch in an edge of the substrate; and a controller adapted to oscillate the substrate between at least first and second oscillatory positions while the polishing head contacts the substrate notch. Numerous other aspects are provided.

The present application claims priority from U.S. Provisional Patent Application Ser. No. 60/939,228, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR POLISHING A NOTCH OF A SUBSTRATE BY SUBSTRATE VIBRATION” (Attorney Docket No. 11952/L), which is hereby incorporated by reference herein in its entirety.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to the following commonly-assigned, co-pending U.S. patent applications, each of which is hereby incorporated herein by reference in its entirety for all purposes:

U.S. patent application Ser. No. 11/299,295, filed on Dec. 9, 2005 and entitled “METHODS AND APPARATUS FOR PROCESSING A SUBSTRATE” (Attorney Docket No. 10121/PPC/CMP/CKIM);

U.S. patent application Ser. No. 11/298,555, filed on Dec. 9, 2005 and entitled “METHODS AND APPARATUS FOR PROCESSING A SUBSTRATE” (Attorney Docket No. 10414/PPC/CMP/CKIM);

U.S. patent application Ser. No. 60/939,351, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR POLISHING A NOTCH OF A SUBSTRATE USING AN INFLATABLE POLISHING WHEEL” (Attorney Docket No. 10674/L);

U.S. patent application Ser. No. 60/939,353, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR FINDING A SUBSTRATE NOTCH CENTER” (Attorney Docket No. 11244/L);

U.S. patent application Ser. No. 60/939,343, filed May 21, 2007, entitled “METHODS AND APPARATUS TO CONTROL SUBSTRATE BEVEL AND EDGE POLISHING PROFILES OF EPITAXIAL FILMS” (Attorney Docket No. 11417/L);

U.S. patent application Ser. No. 60/939,219, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR POLISHING A NOTCH OF A SUBSTRATE USING A SHAPED BACKING PAD” (Attorney Docket No. 11483/L);

U.S. patent application Ser. No. 60/939,342, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR REMOVAL OF FILMS AND FLAKES FROM THE EDGE OF BOTH SIDES OF A SUBSTRATE USING BACKING PADS” (Attorney Docket No. 11564/L);

U.S. patent application Ser. No. 60/939,350, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR USING A BEVEL POLISHING HEAD WITH AN EFFICIENT TAPE ROUTING ARRANGEMENT” (Attorney Docket No. 11565/L);

U.S. Patent Application Ser. No. 60/939,344, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR USING A ROLLING BACKING PAD FOR SUBSTRATE POLISHING” (Attorney Docket No. 11566/L);

U.S. Patent Application Ser. No. 60/939,333, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR SUBSTRATE EDGE POLISHING USING A POLISHING ARM” (Attorney Docket No. 11567/L);

U.S. Patent Application Ser. No. 60/939,212, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR IDENTIFYING A SUBSTRATE EDGE PROFILE AND ADJUSTING THE PROCESSING OF THE SUBSTRATE ACCORDING TO THE IDENTIFIED EDGE PROFILE” (Attorney Docket No. 11695/L);

U.S. Patent Application Ser. No. 60/939,337, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR HIGH PERFORMANCE SUBSTRATE BEVEL AND EDGE POLISHING IN SEMICONDUCTOR MANUFACTURE” (Attorney Docket No. 11809/L); and

U.S. Patent Application Ser. No. 60/939,209, filed May 21, 2007, entitled “METHODS AND APPARATUS FOR CONTROLLING THE SIZE OF AN EDGE EXCLUSION ZONE OF A SUBSTRATE” (Attorney Docket No. 11987/L);

FIELD OF THE INVENTION

The present invention relates generally to substrate processing, and more particularly to methods and apparatus for cleaning a notch in an edge of a substrate.

BACKGROUND OF THE INVENTION

Substrates are used in semi-conductor device manufacturing. During processing, the notch and edge of a substrate may become dirty, which may negatively affect the semi-conductor devices formed on the substrate. Conventional systems may not be able to effectively clean a substrate notch in a cost-effective amount of time. Accordingly, improved methods and apparatus for cleaning or polishing notches in the edges of substrates are desired.

SUMMARY OF THE INVENTION

In a first aspect of the invention, an apparatus for polishing a notch in a substrate edge is provided. The apparatus comprises a substrate support adapted to support a substrate; a polishing head adapted to contact a notch in an edge of the substrate; and a controller adapted to oscillate the substrate between at least first and second oscillatory positions while the polishing head contacts the substrate notch.

In another aspect of the invention, a system for polishing a notch in a substrate edge is provided. The system comprises a substrate support adapted to support a substrate; a polishing head adapted to press a polishing tape against a notch in an edge of the substrate; a controller adapted to oscillate the substrate between at least first and second oscillatory positions while the polishing head contacts the substrate notch to control polishing by the polishing head.

In yet another aspect of the invention, a method for polishing a notch in a substrate edge is provided. The method comprises supporting a substrate, wherein an edge of the substrate includes a notch; pressing a polishing head against a surface of the notch; and oscillating the substrate between first and second oscillatory positions while the polishing head is pressed against the notch.

Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of an embodiment of a system for polishing parts of a substrate, including major surfaces, edge, bevel, and notch in accordance with the present invention.

FIG. 2 is a perspective view of an embodiment of a polishing apparatus for polishing a substrate notch in accordance with the present invention.

FIG. 3 is a perspective view of part of the embodiment of a polishing apparatus for polishing a substrate notch, shown in FIG. 2.

FIG. 4 is a schematic illustration of part of an exemplary substrate, including a substrate notch.

FIG. 5 is a schematic cross-sectional view of an embodiment of a supporting backing pad for polishing a substrate notch in accordance with the present invention.

FIG. 6 is a top plan view of an exemplary substrate.

FIG. 7 is a flow chart of a method for polishing a substrate notch according to an embodiment of the present invention.

DETAILED DESCRIPTION

Substrates used in semiconductor device processing often have films and/or surface defects which typically should be removed prior to subsequent processing steps. In some cases, these films and defects may occur on the edge of a substrate, including a notch formed thereon.

One method of cleaning and polishing a substrate notch includes applying an abrasive film or tape to the notch, and moving the abrasive tape relative to the notch, while the substrate is fixed in a particular position. The force, or pressure, applied to the abrasive tape while contacting the notch, as well as the degree of contact between the abrasive tape and the notch, may contribute to polishing efficiency. Another factor that may contribute to polishing efficiency is the degree of movement of the abrasive tape relative to the substrate notch. In some embodiments, the relative movement may be provided by advancing the abrasive tape over a surface of the notch. However, the degree of relative movement between the abrasive tape and the substrate notch may be increased by moving the substrate as the abrasive tape is advanced over the notch surface, thereby increasing the notch polishing efficiency and the cost-effectiveness thereof.

The present invention provides apparatus and methods that enhance contact between the polishing or abrasive tape and all sections of a substrate notch region to efficiently and cost-effectively remove thin films and surface defects from the substrate notch. In one or more embodiments, a notch backing pad may be provided. The notch backing pad may be adapted to press a moving polishing tape against the substrate notch. In some embodiments, the notch backing pad may include a protruding portion that substantially conforms to the shape of the substrate notch. The protruding portion may be made of an elastically deformable material adapted to effectively conform the notch backing pad to the shape of the notch (e.g., when pressed against the notch), and to press the polishing tape into contact with all surfaces of the notch. The notch backing pad may include slots to guide the polishing tape over the notch backing pad.

In some embodiments, the substrate may be rotated and/or oscillated about a center of rotation as the polishing tape is advanced over the notch. The rotation and/or oscillation may increase the degree of relative movement between the polishing tape and the substrate notch, thereby increasing the polishing efficiency and cost-effectiveness thereof.

FIG. 1 is a schematic plan view depicting an exemplary embodiment of a substrate polishing system 100 according to the present invention. The system 100 of FIG. 1 may be adapted to polish a substrate 102, including, for example, a substrate edge 101 and/or notch 244 (shown in FIG. 3) positioned in the substrate edge 101. In some embodiments, the notch 244 may be used to align the substrate 102 in the system 100. The substrate 102 may also include two major surfaces 103, (one of which is shown). Each major surface 103 of the substrate 102 may include a device region (not shown) upon which devices may be fabricated, and edge exclusion regions (not shown) upon which device fabrication is not meant to occur. (Typically however, only one of the two major surfaces 103 will include a device region and an edge exclusion region). The edge exclusion regions or zones may serve as a buffer between the device regions and the substrate edge 101. In an edge polishing process, the substrate edge 101, including the notch 244, may be polished to remove defects or contaminants, to reduce film thickness and more generally to improve surface uniformity.

The system 100 of FIG. 1 includes three polishing heads 104 which, in turn, may each include a plurality of polishing apparatus for cleaning and polishing the above-mentioned parts of the substrate 102. Any number and type of polishing heads 104 may be used in any practicable combination. Any number of heads 104 may be used concurrently, individually, and/or in any sequence. The one or more heads 104 may be disposed in different positions, and in different orientations (e.g., aligned with the substrate edge or notch, normal to the substrate edge or notch, angled relative to the substrate edge or notch, etc.), to allow the one or more polishing heads 104 (and backing pads and/or polishing tape described further below) to polish different portions of the edge and/or notch of the substrate 102. The substrate 102 may be stationary or rotate as it is polished. The one or more heads 104 may be adapted to be oscillated or moved (e.g., angularly translated about a tangential axis of the substrate 102 and/or circumferentially translated relative to the substrate 102) around or along the substrate edge 101 and/or notch 244 by any suitable means so as to polish different portions of the substrate 102. Different heads 104 may be used for different substrates 102, different types of substrates 102, or different polishing operations.

The system 100 may also include a programmed or user operated controller 106. The controller 106 may direct the operation and movement of the one or more heads 104, as well as the other system components, as will be further described below.

FIG. 2 is a perspective view of an embodiment of a polishing apparatus 200 for polishing a substrate notch 244 (shown in FIG. 3). The polishing apparatus 200 may include a substrate driver 210 (e.g., a servomotor, gear, belt, chain, etc.), which may be mounted on a pedestal 212. A support 214 (e.g., a vacuum chuck) may be coupled (e.g., rigidly) to a shaft (not shown) of the substrate driver 210. The support 214 may support a substrate 216, for example. The substrate driver 210 may rotate the substrate 216, via the support 214, about a center 218 of the substrate 216 or another suitable axis. The substrate driver 210 may be connected to a substrate driver control unit (not shown), which may control the angular displacement, angular velocity, and angular acceleration of the substrate 216. The polishing apparatus 200 may further include a polishing arm 220 aligned in the horizontal plane approximately tangential to the edge 103 (shown in FIG. 1) of the substrate 216 and supported by a frame 224. In other embodiments, the polishing arm 220 may be aligned differently, for example, vertically or at an angle with respect to the horizontal plane. The polishing arm 220 may include a polishing head section 222. The polishing head 222 may include a notch backing pad 226, which may be moved toward or away from the substrate 216 by an actuator (e.g., hydraulic actuator, pneumatic actuator, servomotor, etc.) (not shown). Polishing tape 228, may wrap around the polishing head 220, and over the notch backing pad 226, and be tensioned between spools 230, 232. The spools 230, 232 may be driven by spool drivers 234, 236 (e.g., servomotors), respectively. The spool drivers 234, 236, may be indexed to precisely control the amount of the polishing tape 228 that is advanced over the polishing head 220 from, for example, spool 230 to spool 232 in order to polish the notch 244 in the substrate 216.

In one or more embodiments, the polishing tape 228 may be made from many different materials, such as aluminum oxide, silicon oxide, silicon carbide, etc. Other materials may also be used. In some embodiments, abrasives used may range from about 0.5 microns up to about 3 microns in size, although other sizes may be used. Different widths of polishing tape 228 ranging from about 0.2 inches to about 1.5 inches may be used, although other polishing tape widths may be used. In one or more embodiments, the polishing tape 228 may be about 0.002 to about 0.02 inches thick and withstand about 1 to 5 lbs. in tension. Other tapes having different thicknesses and tensile strengths may be used. The spools 230, 232 may have a diameter of approximately 1 inch and be capable of holding about 500 inches of polishing tape 228. Other spool dimensions may be used. The spools 230, 232 may be constructed from materials such as polyurethane, polyvinyl difluoride (PVDF), etc. Other materials may also be used.

FIG. 3 is a perspective view of part of the embodiment of the polishing apparatus 200 shown in FIG. 2 for polishing the substrate notch 244. The polishing head 222, supported by the polishing arm 220, may include the notch backing pad 226 and one or more guide rollers 238, 240. In some embodiments, the polishing tape 228 may wrap around the polishing head 222 by wrapping around one of the guide rollers 238, the notch backing pad 226 and another of the guide rollers 240. As described above, the polishing tape 228 may be tensioned between spool 230 and 232. In some embodiments the notch backing pad 226 may include a protruding portion 242, having a cross section similar in shape to the substrate notch 244. The polishing tape 228 may be positioned to conform to the shape of the protruding portion 242 of the notch backing pad 226 when wrapped around the polishing head 220, and tensioned between the spools 230, 232.

As described above, the notch backing pad 226 may be moved toward, or away from, the substrate 216 by an actuator (not shown). Any other suitable means to move the notch backing pad 226 may be used. When the notch backing pad 226 is moved toward the substrate 216, the protruding portion 242 of the notch backing pad 226 may be pressed into the substrate notch 244. As the protruding portion 242 is pressed into the notch 244, the section of polishing tape 228 conforming to the shape of the protruding portion 242 of the notch backing pad 226 is also pressed into, and conforms to, the substrate notch 244, and thereby contacts the entire substrate notch 244 surface. As the polishing tape 228 may contact the entire surface of the substrate notch 244, as the polishing tape 228 is advanced, it may clean and polish the entire surface of the substrate notch 244.

With reference to FIG. 4, a part of the substrate 216 including the notch 244 is schematically illustrated. The size of the notch 244 is exaggerated for clarity purposes. The notch 244 may include one or more notch sides 400. The notch 244 may also include one or more notch corners 402. Each notch corner 402 may be positioned at the intersection of a notch side 400 and the outer perimeter of the substrate 216. The notch 244 may further include a notch center 404, positioned at the intersection of the one or more notch sides 400. A notch depth 406 may be calculated as the length or distance between the horizontal plane of the notch center 404 and the horizontal plane of the notch corners 402. In some embodiments, for example, in the embodiment shown herein, the notch 244 may exhibit a large change in curvature as it is traced from one notch corner 402 to another notch corner 402, via the notch sides 400 and notch center 404. The change in curvature of the notch 244 geometry may make it desirable to maintain consistent contact between the polishing tape 228 and all regions (e.g., notch sides 400, notch corners 402, and notch center 404) of the notch 244 during polishing, such that the entire notch 244 may be polished/cleaned.

FIG. 5 is a schematic cross-sectional view of an exemplary embodiment of the notch backing pad 226 adapted to polish the substrate notch 244. As described above, the notch backing pad 226 may include the protruding portion 242, whose shape roughly corresponds to the shape of the substrate notch 244. In some embodiments, the protruding portion 242 may be made of a soft conforming material, such as polyurethane, or any other suitable material. In other embodiments, the protruding portion 242 may be made of a rigid material. The rest of the notch backing pad 226 may be made of soft, conforming materials, or rigid materials. The notch backing pad 226 may also include one or more slots 246, 248. The slots 246, 248 may guide the polishing tape 228 over the protruding portion 242, as the polishing tape 228 is advanced and contacts the substrate notch 244. When the protruding portion 242 of the notch backing pad 226 is pressed into the notch 244, the protruding portion 242 may conform to the shape of the notch 244, and thereby cause the polishing tape 228 to contact the notch sides 400, the notch corners 402 and the notch center 404 (FIG. 4).

Turning to FIG. 6, a top plan view of an exemplary embodiment of substrate oscillating in the notch polishing apparatus of the present invention. It should be noted that the notch 244 shown herein is not drawn to scale, and is enlarged for illustrative purposes. As described above with respect to FIGS. 1 and 2, the substrate 216 may be supported by the support 214, and rotated and/or oscillated about the substrate center 218 by the substrate driver 210. For example, the controller 106 (FIG. 1) or another controller may cause the substrate driver 210 to rotate back and forth so as to rotate (e.g., oscillate) the substrate 216 back and forth. To polish the substrate notch 244, the polishing tape 228 may be advanced over the notch backing pad 226, as the polishing tape 228 contacts the notch 244, via pressure from the notch backing pad 226. The direction of polishing tape 228 advancement as the polishing tape 228 contacts the notch 244 may be approximately perpendicular to a plane of rotation of the substrate 216, i.e., approximately normal to the figure. However, the polishing tape 228 may be advanced at other angles with respect to the plane of rotation of the substrate 216.

In some embodiments, as the polishing tape 228 is advanced, the substrate 216 may be rotated or oscillated sinusoidally or otherwise about its center 218. For example, the controller 106 (FIG. 1) may cause the substrate driver 210 to rotate back and forth. In the exemplary embodiment shown herein, the substrate 216 is oscillated about its center of rotation 218. Radius R indicates a direction in which the substrate notch 244 is aligned with, or approximately centered with respect to, the polishing head 222 (not shown in FIG. 6, shown in FIG. 2) and, specifically, the protruding portion 242 of the notch backing pad 226 (see FIG. 5). As the substrate 216 is oscillated, radius R may indicate a neutral position or direction of the substrate 216, and radii R₁ and R₂ may indicate limits of travel of the notch center 204 (shown in FIG. 4) as the substrate is oscillated through angles θ₁ and θ₂, respectively. Dotted line 244 a indicates an outline of the notch 244 at one limit of travel R₁, and dotted line 244 b indicates an outline of the notch 244 at another limit of travel R₂. The angles of rotation θ₁ and θ₂ of the substrate 216 may be set approximately equal to one another, or they may be set different from one another. Each angle θ₁, θ₂ may range between approximately 0 degrees and approximately 1 degree during polishing in some embodiments. Other angles may be used. A frequency of oscillation of the substrate 216 between radii R₁ and R₂ may be varied, for example, from approximately 0 cycles/min to approximately 50,000 cycles/min during polishing, and preferably from approximately 1000 cycles/min to approximately 50,000 cycles/min during polishing. Other and/or a constant number of cycles per minute may be used.

The force or pressure at which the polishing tape 228 is pressed against the notch 244, as well as the relative movement of the polishing tape 228 and the notch 244 may account for the degree and/or efficiency of polishing. The advancement of the polishing tape 228, for example, in a direction perpendicular to the major surface of the substrate 216, as it contacts the notch 244 may provide relative movement between the polishing tape 228 and the notch 244, thereby aiding in the polishing process. In addition, oscillation of the substrate 216 about the substrate center 218 during the advancement of the polishing tape 228 may provide further relative movement between the polishing tape 228 and a surface of the notch 244, thereby aiding in the polishing process. In some embodiments, the combination of substrate oscillation with polishing tape advancement may result in more effective notch polishing than the use of polishing tape advancement alone, as the oscillation creates greater contact between the polishing tape 228 and the notch surfaces.

Turning to FIG. 7, an exemplary method 700 for cleaning and polishing the notch 244 in the substrate 216 is depicted. In step S702, the substrate 216 may be positioned and secured on the support 214. Then, in step S704, the substrate 216 may be rotated until the notch 244 is aligned with the polishing head 222, e.g., aligned with the protruding portion 242 of the notch backing pad 226. In step S706, the protruding portion 242 of the notch backing pad 226 contacts the substrate notch 244, and presses the polishing tape 228 against the notch 244. In step S708, the polishing tape 228 may be advanced by spool driver 234 or spool driver 236, e.g., either of spools 230, 232 may be used as a take-up spool or a supply spool. In step S710, the substrate 216 may be oscillated about its center 218 or another suitable point. This step may be performed simultaneously with, before, or after step S708. Advancement of the polishing tape 228 as it contacts the notch 244, in combination with the oscillation of the substrate 216, removes and eliminates films and imperfections on the notch 244 via abrasion.

In addition, in step S712, the polishing head 222 may be vertically rotated or rocked about the notch 244, e.g., the polishing head 222 may rotate about an axis tangential to the substrate 216 (and hence notch 244), as the polishing tape 228 is advanced, in order to more effectively clean and polish parts of the notch 244 adjacent to major surfaces 103 (shown in FIG. 1) of the substrate 216. Step S712 may be performed simultaneously with, before or after step S708 and/or S710. The speed, direction, tension, pressing force, etc., of the polishing tape 228, the rotational displacement, speed, and acceleration of the substrate 216, and the rotational displacement, speed, and acceleration of the polishing head 222 about the substrate 216, may be adjustable, via, for example, the controller 106 (FIG. 1). For instance, the polishing tape 228 may be advanced at one speed for a certain length, and then another speed for another length. In addition, the polishing tape 228 may be at least one of translated and oscillated, with constant or variable tensions and pressing forces. Furthermore, the substrate 216 may be oscillated at a first amplitude for a first period of time and a second amplitude for a second period of time. Additionally or alternatively, the substrate 216 may alternate between time periods of oscillation and time periods of simple or no rotation. Substrate oscillation may also be employed during cleaning of an edge region of a substrate which does not include a notch (e.g., using similar or other oscillations).

The foregoing description discloses only exemplary embodiments of the invention. Modification of the above disclosed apparatus and methods which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art.

Accordingly, while the present invention has been disclosed in connection with exemplary embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claim. 

1. An apparatus for polishing a notch in a substrate edge comprising: a substrate support adapted to support a substrate; a polishing head adapted to contact a notch in an edge of the substrate; and a controller adapted to oscillate the substrate between at least first and second oscillatory positions while the polishing head contacts the substrate notch.
 2. The apparatus of claim 1 wherein the polishing head includes a backing pad.
 3. The apparatus of claim 2 further comprising a polishing tape, wherein the backing pad is adapted to contact the substrate notch with the polishing tape.
 4. The apparatus of claim 3 further comprising a motor adapted to advance the polishing tape, thereby creating relative movement between the polishing tape and the substrate notch.
 5. The apparatus of claim 2 wherein the backing pad includes a protruding member.
 6. The apparatus of claim 5 wherein the protruding member is adapted to be pressed into the substrate notch.
 7. The apparatus of claim 5 wherein the protruding member is conformable to the shape of the substrate notch.
 8. The apparatus of claim 1 wherein the first oscillatory position is at a first oscillatory angle to a neutral radius of the substrate when the substrate is stationary.
 9. The apparatus of claim 8 wherein the second oscillatory position is at a second oscillatory angle to a neutral radius of the substrate when the substrate is stationary.
 10. The apparatus of claim 9 wherein the first oscillatory angle is the same as the second oscillatory angle.
 11. The apparatus of claim 9 wherein the frequency of oscillation between the first and second oscillatory positions is varied.
 12. The apparatus of claim 1 wherein the polishing head is adapted to rock about an axis tangential to the substrate notch.
 13. A system for polishing a notch in a substrate edge comprising: a substrate support adapted to support a substrate; a polishing head adapted to press a polishing tape against a notch in an edge of the substrate; a controller adapted to oscillate the substrate between at least first and second oscillatory positions while the polishing head contacts the substrate notch and to control polishing by the polishing head.
 14. The system of claim 13 wherein the polishing head includes a backing pad.
 15. The system of claim 14, wherein the backing pad is adapted to contact the substrate notch with the polishing tape.
 16. The system of claim 15 further comprising a motor, wherein the motor is adapted to advance the polishing tape, thereby creating relative movement between the polishing tape and the substrate notch.
 17. The system of claim 13 wherein the first oscillatory position is at a first oscillatory angle to a neutral radius of the substrate when the substrate is stationary.
 18. The system of claim 19 wherein the second oscillatory position is at a second oscillatory angle to a neutral radius of the substrate when the substrate is stationary.
 19. The system of claim 13 wherein the substrate oscillates at a first amplitude for a first period of time and at a second amplitude for a second period of time.
 20. A method for polishing a notch in a substrate edge comprising: supporting a substrate, wherein an edge of the substrate includes a notch; pressing a polishing head against a surface of the notch; and oscillating the substrate between first and second oscillatory positions while the polishing head is pressed against the notch.
 21. The method of claim 20 further comprising pressing a polishing tape against the notch via the polishing head.
 22. The method of claim 21 further comprising advancing the polishing tape as the polishing tape is pressed against the notch.
 23. The method of claim 20 further comprising rocking the polishing head about the notch.
 24. The method of claim 20 further comprising conforming the polishing head to the shape of the notch.
 25. The method of claim 20, wherein the polishing head includes a backing pad adapted to conform to the shape of the notch. 